[GPU] Decompress GBGR/BGRG into RGBB, not RGB1

While the alpha of the texture data is not used at all (replaced with blue using the view swizzle), still make the shader code state the intention more explicitly if the format is decompressed for use as signed. Unsigned 1.0 is 0xFF, while signed 1.0 is 0x7F.

src/xenia/gpu/d3d12/d3d12_texture_cache.h

@@ -190,9 +190,9 @@ class D3D12TextureCache final : public TextureCache {
     kR5G5B6ToB5G6R5WithRBGASwizzle,
     kR4G4B4A4ToB4G4R4A4,
     kGBGR8ToGRGB8,
-    kGBGR8ToRGBA8,
+    kGBGR8ToRGB8,
     kBGRG8ToRGBG8,
-    kBGRG8ToRGBA8,
+    kBGRG8ToRGB8,
     kR10G11B11ToRGBA16,
     kR10G11B11ToRGBA16SNorm,
     kR11G11B10ToRGBA16,